A junction field effect transistor (JFET) made of silicon (Si) is the preferred component for all applications that require high input impedance and low noise level in the low frequency range. Typically, its equivalent input noise level is about 1 nanovolt per hertz (1 nV/Hz) at 1 kilohertz (kHz). Nevertheless, JFETs cannot operate at cryogenic temperatures, below about 40 kelvins (K), and below about 100 K, a clear degradation is observed in their performance in terms of transconductance and noise level. In this context, reference may be made to the article by F. Ayela et al. “Noise measurements on silicon JFETs at low temperature using a very high Q superconducting resonator”, Rev. Sci. Instrum. 62 (11), November 1991, pp. 2816-2821.
The coupling between a detector cooled to cryogenic temperature and its JFET acquisition electronics must therefore be made via a cable, which introduces additional noise and which presents capacitance that reduces acquisition speed.
JFETs and metal-semiconductor field effect transistors (MESFETs) made of GaAs constitute an alternative to silicon JFETs for cryogenic applications. The performance of such components is described in the article by R. K. Kirschman and J. A. Lipa “Further evaluation of GaAs FETs for cryogenic read-out”. Their low frequency noise level is typically higher than that of Si JFETs.
HEMTs can operate equally well at room temperature and at low temperature. These devices present excellent performance in the microwave frequency range, but they present a relatively high noise level at frequencies of less than about 1 gigahertz (GHz). In this respect, reference may be made to:
R. Plana et al. “Noise in AlGaAs/InGaAs/GaAs pseudomorphic HEMTs from 10 Hz to 18 GHz”, IEEE Transactions on Electron Devices, Vol. 40, No. 5, May 1993; and
E. Grémion et al. “Development of ultra-low noise HEMTs for cryoelectronics at ≦4.2 K”, J. Low Temp. Phys. (2008) 151, pp. 971-978.
In addition, their gate leakage current is much greater than that of JFETs. Several alternative solutions have been proposed for reducing the gate current of HEMTs, in this context, reference may be made to the following articles:
S. Mizuno et al. “Large gate leakage current in AlGaN/GaN high electron mobility transistors”, Jpn. J. Apl. Phys. Vol. 41 (2002), pp. 5125-5126;
H. C. Lin et al., “Enhancement-mode GaAs metal-oxide-semiconductor high-electron-mobility transistors with atomic layer deposited Al2O3 as gate dielectric”, Applied Physics Letters 91, 212101 (2007); and
A. Nagayama et al. “Suppression of gate leakage current in n-AlGaAs power HEMTs”, IEEE Transactions on Electron Devices, Vol. 47, No. 3, March 2000.
The use of those solutions is found to be complex and does not enable a noise level to be reached that is as low as that of silicon JEFTs.